*B 


323 


EXCHANGE 


A    Study    of    tlie    Composition    of    an 

Ammonium  Pkospkomolykdate  and 

tke   Determination   ox 

Phosphorus. 


DISSERTATION 

SUBMITTED     IN     PARTIAL    FULFILMENT     OF    THE    REQUIRE- 
MENTS  FOR  THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY 
*    IN  THE  FACULTY  OF  PURE  SCIENCE  IN 
COLUMBIA  UNIVERSITY 


BY 
NORMA  E.  JOHANN,  A.B.,  A.M. 


New  York  City 
1921 


^ 


The  Jackson  Press,  Kingston 
1921 


A    Study    oi    tlie    Composition    of    an 

Ammonium  PkosphomolyLdate  and 

tne   Determination   or 

Phosphorus. 


DISSERTATION 

Submitted  in  partial  fulfillment  of  the  requirements  for  the  degree 

of  Doctor  of  Philosophy  in  the  Faculty  of  Pure  Science, 

Columbia  University 


BY 

NORMA  E.  JOHANN,  A.B.,  A.M. 

n 

New  York  City 
1921 


The  Jackson  Press,  Kingston 
1921 


•      •   *      *   ••  •      »     •  •  •  •         .       *       • *  * 

•  •••£•  5  •*•"••     •  ••       * 


ACKNOWLEDGMENT 

The  author  wishes  to  express  her  appreciation  of  the  interest 
and  advice  given  throughout  this  investigation  by  Professor  H.  T. 

Beans,  at  whose  suggestion  it  was  undertaken. 

N.  E.  J 


A  STUDY  OF  THE  COMPOSITION  OF  AN  AMMONIUM 
PHOSPHOMOLYBDATE  AND  THE  DETERMINA- 
TION OF  PHOSPHORUS 

In  view  of  the  conflicting  statements  found  in  the  literature 
regarding  the  composition  of  the  ammonium  phosphomolybdate 
precipitate,  it  was  decided  to  try  once  more  to  analyse  this  precipi- 
tate and  to  determine,  if  possible,  the  conditions  for  obtaining  a 
precipitate  of  constant  composition. 

Following  are  given  some  of  the  analyses  of  ammonium  phos- 
phomolybdate for  phosphorus  pentoxide  and  molybdic  oxide  found 
in  the  literature  together  with  the  method  of  treating  the  precipitate. 
In  many  cases  the  methods  of  analysis  are  not  given. 

Author          Method  of  treating  ammonium  Ratio 

phosphomolybdate  precipitate   P205          Mo03      P205:Mo03 

Nutzinger1     dried  at  100° C 3.82%  92.70%  1:23.92 

Seligsohn2     dried  at  100° C 3.142  90.744  1:28.48 

Sopp3 3.20  86.0  1:26.50 

Struve  &  Svanberg4 3.63  86.88  1:23.60 

Sonnenschein5    3.03  86.87  1:28.27 

Macagno6     dried  at  100°C 3.142  90.744  1:28.48 

Rammelsberg7     dried  at  100° C 3.90  86.45  1:21.85 

Gibbs8     dried   by    pressing  with   woolen 

paper 3.70&  89.00  1:23.72 

3.83 
Hundeshagen9     washed  with  dilute  HN03 

dried  at  130-150 °C 3.72&  91.86  1:24.35 

Babbitt10    washed  with   water,   dried   at  3.77  92.11  24.10 

85-90°C.  for  3  days 3.724  90.315  1:23.92 

Doolittle  &  Eavensen11     dried  to  constant 

weight  at  130° C.  3.76  91.65  1:24.00 

iJahresb,  1855,  374. 

2J.  f.  Prakt.  Chem.  67,  470. 

3Pogg.  Annal.  109,  136. 

4Jahresb,  1847,  412. 

5J.  f.  Prakt.  Chem.  53,  342  (1851). 

6Chem.  News  31,  197  (1875). 

7Ber.  10,  1776  (1877). 

8Am.  Chem.  Jour.  3,  317  (1881). 

»Z.  f.  Anal.  Chem.  28,  141,  (1889). 

10J.  Anal,  and  Appl.  Chem.  7,  165  (1893). 

"Jour.  Am.  Chem.  Soc.  16,  234   (1894). 


451720 


Blair  &  Whitfield12     dried   at   100°C.   for 

12  hours   3'59  88.06  1:24.19 

dried  over  KOH  for 

3  months 3.59  88.06  1:24.19 

Gladding13     washed  with  1%  HNO3,  dried 

to  constant  weight  at  105° C    3.76  91.36  1:23.96 

Baxter14  washed  with  10%  NH4N03, 
heated  to  constant  weight  at 
300°C 3.7422  92.16  1:24.29 

Hundeshagen  says  that  the  composition  of  the  precipitate  after 
washing  with  cold  dilute  nitric  acid  and  drying  at  130-1 50° C.  cor- 
responds to  the  formula  (NH4)3PO4  .  12  MoO3  whether  precipitated 
in  nitric,  hydrochloric  or  sulphuric  acid  solutions  containing  ammo- 
nium salts.  The  precipitate  obtained  with  excess  acid,  washed  with 
cold  dilute  acid  and  dried  in  a  desiccator  contains,  according  to  the 
acid,  two  molecules  of  HNO3  or  HC1  with  one  molecule  of  H2O 
probably  in  unstable  chemical  combination.  This  formula 
(NH4)3PO4  .  12  MoO3  of  the  dried  precipitate  is  the  one  now  most 
generally  accepted.  It  corresponds  to  3.783%  P2O5  and  92.06% 
Mo03. 

Finkener  (Ber.  11,  1638  (1878)  was  one  of  the  first  to  point 
out  that  the  ratio  of  P2O5  to  MoO3  is  1 : 24  and  not  1 : 20  as  given 
by  Debray  (Chem.  News  17,  183  (1868)  or  1 : 22  as  given  by  Ram- 
melsberg.  He  and  also  Auld  (Analyst  37,  130  (1912)  state  that 
the  variation  in  composition  is  due  to  variation  in  the  amount  of 
ammonia  and  water  in  the  molecule.  The  work  of  the  present  in- 
vestigation confirms  this  statement.  Wolcott  Gibbs  believed  that 
there  are  three  classes  of  phosphomolybdates.  He  prepared  and 
analysed  three  in  which  the  ratio  of  P2  O5  to  MoO3  was  1 :  20,  1 :  22, 
1 : 24.  It  may  be  possible  to  have  a  mixture  of  the  three  classes  of 
salts.  Hissink  and  von  der  Waerden  (Chem.  Weekblad  2,  179 
(1905)  have  proposed  a  formula  requiring  12.65  molecules  of  MoO3 
per  molecule  of  phosphomolybdate  and  Wardlaw  ( J.  Pro.  Roy.  Soc. 
N.  S.  Wales-4S,  Part  I,  73  (1914),  12.75. 

A  large  number  of  investigators  have  determined  phosphorus 
by  weighing  either  the  dried  precipitate  (NH4)3PO4  .  12  MoO3  or 
the  compound  P2O5  .  24  MoO3,  obtained  by  ignition  of  the  phos- 
phomolybdate under  various  conditions.  Following  are  some  of 
the  factors  given  for  these  procedures. 

12 Jour.  Am.  Chem.  Soc.  17,  747  (1895). 
13Jour.  Am.  Chem.  Soc.  18,  23  (1896). 
14Am.  Chem.  Jour.  28,  298  (1902). 


Factor 

Author  Method  of  treating  precipitate  to  P2O_ 

Finkener15     washed  with  NH4NO3,  heated  to  160-180  °C 0.03794 

Hehner16     washed   with   alcohol,    dissolved   in    NH4OH    evap- 
orated solution,  dried  at  100 °C 0.03509 

Tamm17     washed  with  1%  HNO3,  dried  at  120° C 0.0376 

Wood18     washed  with  dilute  HN03,  dried  at  100°C 0.0373 

ignited 0.0396 

Carnot19     washed  with  H2O,  dried  at  100° C 0.0373 

Villiers  &  Borg20     dried  at  100  °C.  for  6  hrs 0.03728 

,Meineke21     washed  with  H2O,  alcohol,  ether,  and  ignited 0.03949 

Gladding13  washed  with  1%  HN03,  dried  at  105°C 0.0376 

Woy2^     washed  with  1%NH4N03  +  HNO3, 

ignited  -»  P2O5  .  12MoO3   0.03946 

Lorenz23     washed  with  2%  NH4NO3,  alcohol,  ether,  dried    in 

vacuum 0.03295 

Baxter14  washed  with  10%  NH4NO3,  heated  to  constant  weight 

at300°C 0.03742 

Raben24     washed  with  alcohol,  dried  at  110-120°C 0.0375 

Christensen25     ignited — assumed  P2O5  .  24Mo03  0.0394 

Jorgensen26     heated,  not  too  strongly  to  P2O5  .  24MoO3 0.0394 

Chesneau27     dried  at  105°C 0.0366 

ignited 0.0387 

Maude28     ignited 0.039467 

Auld29     washed  with  1%  HNO3,    dried,    ignited    to    constant 

weight °. 0.0396 

Neubauer  &  Lucker30    washed  with  2%  NH4NO3,  acetone 0.03295 

The  wide  variation  in  the  factors  proposed  even  when  the  con- 
ditions are  nearly  identical  and  the  many  conditions  of  treatment 
which  have  been  suggested  show  conclusively  that  analysts  have 
encountered  difficulties  in  the  application  of  those  procedures  in- 
volving the  drying  or  ignition  of  the  phosphomolybdate  precipitate. 

With  a  view  to  overcoming  some  of  the  difficulties  and  uncer- 
tainties of  the  gravimetric  method,  various  volumetric  procedures 

15Ber.  11,  1638  (1878). 
"Analyst^,  23  (1879). 
17Chem.  News  49,  208  (1884). 
18 Jour.  Anal.  Chem.  1,  138  (1887). 
19Chem.  News  67,  101  (1893). 
20Comptes  Rendus  116,  989  (1893). 
21Chem.  Ztg.  20,  108  (1896). 
22Chem.  Ztg.  21,  441   (1897). 
23Z.  f.  Anal.  Chem.  46,  193  (1907). 
24Z.  f.  Anal.  Chem.  47,  546   (1908). 
25Z.  f.  Anal.  Chem.  47,  529  (1908). 
26Z.  f.  Anal.  Chem.  46,  370   (1907). 
27Comptes  Rendus  146,  758  (1908). 
28Chem.  News  101,  241  (1910). 
29 Analyst  37,  130  (1912). 
3°Z.  f.  Anal.  Chem.  51,  161  (1912). 


have  been  proposed.  The  method  most  generally  used  is  an  acidi- 
metric  one  in  which  the  phosphomolybdate  precipitate  washed  free 
of  acid  is  dissolved  by  the  addition  of  a  measured  excess  of  standard 
alkali  and  the  excess  is  titrated  back  with  standard  acid.  Here 
again  wide  variation  is  encountered  in  the  statements  of  the  authors 
as  to  the  numbers  of  moles  of  alkali  equivalent  to  one  mole  of 
phosphomolybdate  precipitate.  The  values  most  frequently  given 
are  23,  26  or  28  moles  of  alkali  per  mole  of  precipitate. 

Thilo  (Cherri.  Ztg.  11,  193  (1887)  dissolved  the  yellow  precipi- 
tate in  ammonium  hydroxide  titrated  back  with  sulphuric  acid  using 
litmus  as  indicator.  His  ammonium  hydroxide  solution  contained 
32  g.  NH3  per  liter  when  1  cc.  was  equivalent  to  .0669  g.  of  preci- 
pitate. Rothberg  and  Auchinvole  (J.  Anal,  and  Appl.  Chem.  6, 
243  (1892)  washed  the  precipitate  with  1%  nitric  acid  solution,  then 
writh  potassium  nitrate  to  remove  the  free  acid,  dissolved  it  in  a 
standard  sodium  hydroxide  solution  and  titrated  back  the  excess 
with  nitric  acid  using  phenolphthalein  as  the  indicator.  Manby 
(J.  Anal,  and  Appl.  Chem.  6,  82  (1892)  and  Handy,  (J.  Anal,  and 
Appl.  Chem.  6,  204,  (1892)  used  this  same  method,  standardizing 
their  alkali  against  the  pure  precipitate  or  a  steel  of  known  phos- 
phorus content.  Pemberton  (J.A.C.S.  15,  382  (1893),  16,  278 
(1894)  was  the  first  to  make  an  extended  investigation  of  this 
method.  He  agrees  with  Hundeshagen  that  23  molecules  of  alkali 
are  required  for  one  molecule  of  ammonium  phosphomolybdate. 
Kilgore  (J.A.C.S.  16,  765  (1894),  17,  950  (1895)  modified  Pem- 
berton's  method  in  that  he  precipitated  the  phosphomolybdate  at 
60° C.  instead  of  at  boiling  temperature  as  Pemberton  did.  Kilgore 
washed  the  precipitate  with  1%  nitric  acid  solution,  then  with  a  3% 
potassium  nitrate  solution  and  finally  with  water.  He  dissolved  the 
precipitate  in  standard  potassium  hydroxide  solution  and  titrated 
back  the  excess  with  nitric  acid  using  phenolphthalein  as  the  indi- 
cator. Various  other  modifications  of  the  Pemberton-Kilgore 
method  have  been  suggested. 

Lagers  (Z.  f.  Anal.  Chem.  47,  561  (1908)  believes  that  the 
formula  for  the  ammonium  phosphomolybdate  precipitate  is 
(NH4)3PO4  .  12.65  MoO3  which  requires  24.30  molecules  of 
sodium  hydroxide  for  neutralization. 

The  existing  uncertainty  of  the  composition  of  the  phospho- 
molybdate precipitate  and  the  conflicting  statements  found  in  regard 
to  the  volumetric  method,  make  this  volumetric  method  unsatisfac- 
tory as  well  as  the  direct  gravimetric  method.  One  difficulty  in  the 


— 7— 

volumetric  method  is  that  the  end-point  is  not  sharp.  This  may  be 
due  to  several  causes,  as,  for  instance,  the  ammonia  or  phosphate 
present  in  the  solution  of  the  ammonium  phosphomolybdate  preci- 
pitate. 

The  presence  of  ammonia  was  believed  to  cause  interference 
with  the  end-point  when  phenolphthalein  is  used  as  the  indicator  by 
Neumann  (Z.  Physiol.  Chem.  37,  115  (1903),  who  obtained  cor- 
rect results  only  when  he  dissolved  the  precipitate  in  sodium  hy- 
droxide solution,  boiled  out  the  ammonia  and  then  titrated  back 
the  excess  alkali  with  sulphuric  acid  using  phenolphthalein  as  the 
indicator.  In  this  case  one  molecule  of  phosphorus  pentoxide  was 
equivalent  to  56  molecules  of  sodium  hydroxide. 

Neumann's  method  has  been  found  unsatisfactory  by  some 
authors  among  whom  are  Gregersen  (Z.  Physiol.  Chem.  53,  453 
(1907),  Taylor  and  Miller  (J.  Biol.  Chem.  18,  215  (1914),  and 
Kleinmann  (Biochem.  Zeitschr.  99,  19  (1919).  Falk  and  Sugiura 
(J.A.C.S.  37,  1507  (1915)  also  studied  Neumann's  method.  They 
remove  the  ammonia  either  by  boiling  or  by  adding  formaldehyde. 
Heubner  (Biochem.  Zeit.  64,  393  (1914)  used  Neumann's  method 
with  Gregersen's  modification.  These  authors  give  the  factor 
1  cc.  n/2  NaOH  is  equivalent  to  0.553  mg.  phosphorus  (theoretical) 
while  Heubner  used  0.57.  Jodidi  (J.A.C.S.  37,  1708  (1915)  also 
used  Gregersen's  modification  giving  0.57  as  the  factor. 

Wardlaw  (J.  Pro.  Roy.  Soc.  N.  S.  Wales  48,  Part  I,  73  (1914) 
makes  the  statement,  which  the  present  investigation  confirms,  that 
neither  Neumann's  method  nor  any  one  of  the  modifications  gives 
correct  results.  The  amount  of  phosphorus  calculated  from  an 
acidimetric  titration  is  in  every  case  too  high,  the  error  increasing 
with  the  amount  of  phosphorus  present. 

The  object  of  the  present  investigation  is,  therefore,  to  make  a 
more  accurate  determination  of  the  composition  of  the  ammonium 
phosphomolybdate  precipitate,  to  determine  the  conditions  for  ob- 
taining a  precipitate  of  constant  composition,  to  establish  the  proper 
conditions  for  the  acidimetric  method  and  thus  to  propose  the  best 
method  for  the  determination  of  phosphorus.  The  investigation  will 
be  presented  under  the  following  headings :  Preparation  of  Ma- 
terials ;  Composition  of  the  Ammonium  Phosphomolybdate  Precipi- 
tate, (a)  The  Molecular  Ratio  of  phosphorus  pentoxide  to  molybdic 
oxide,  (b)  The  Presence  of  Acid  in  the  Molecule;  New  Method  for 
the  precipitation  of  Ammonium  Phosphomolybdate;  Volumetric 
Method. 


PREPARATION  OF  MATERIALS 

Potassium  dihydrogen  phosphate,  KH2PO4. 

As  a  standard  substance  for  obtaining  a  known  weight  of  phos- 
phorus, potassium  dihydrogen  phosphate  was  used.  This  salt  was 
chosen  because  it  can  easily  be  recrystallized,  it  contains  no  water 
hydration,  and  can  be  dried  to  constant  weight  giving  a  definite 
compound,  KH2PO4.  Its  purity  can  also  be  tested  by  igniting  a 
given  weight  to  metaphosphate.  The  commercial  salt  was  recrystal- 
lized  several  times  and  dried  at  110°C.  Portions  of  known  weight 
were  then  ignited  to  metaphosphate  with  the  following  results : 

Weight  of  KH2PO4    Weight  of  KPO3  Weight  of  KP03  Difference 

calculated  found 

4. 2054  g.             3. 6489  g.  3. 6480  g.  —  .0009g. 

3.5075                 3.0434  3.0425  —.0009 

3.8746                3.3619  3.3613  —.0006 

Molybdic  oxide,  MoOz. 

Due  to  the  uncertainty  of  the  formula  of  ammonium  molybdate 
and  to  the  volatility  of  molybdic  oxide  at  the  temperature  of  the 
decomposition  of  ammonium  molybdate,  it  is  not  possible  to  obtain 
a  known  weight  of  molybdic  oxide  from  a  given  weight  of  ammo- 
nium molybdate.  It  was  therefore  necessary,  for  the  purpose  of 
mixing  known  weights  of  phosphate  and  molybdic  oxide,  to  prepare 
the  latter.  This  was  done  by  treating  small  portions  of  pure  ammo- 
nium molybdate  with  concentrated  nitric  acid  in  a  porcelain  crucible, 
evaporating  to  dryness  and  igniting  gently  with  a  Bunsen  flame. 
More  nitric  acid  was  then  added  and  the  evaporation  and  ignition 
repeated  whereupon  pure  MoO3  was  obtained. 

Molybdate  precipitating  reagent. 

The  usual  molybdate  precipitating  reagent  was  not  used  for 
reasons  given  later.  In  all  the  precipitations  of  phosphorus  here 
described  the  precipitating  reagent  was  prepared  by  dissolving  100 
grams  of  ammonium  para  molybdate  in  400  cc.  of  water  and  80  cc.  of 
concentrated  ammonium  hydroxide.  A  second  solution  was  pre- 
pared consisting  of  400  cc.  of  concentrated  nitric  acid  and  600  cc. 
of  water.  The  required  quantity  of  solution  I  was  poured  into  the 
corresponding  quantity  of  solution  II  just  before  using. 

Ammonium  phosphomolybdate. 

The  yellow  precipitate,  ammonium  phosphomolybdate,  was  pre- 
pared by  precipitating  the  phosphorus  in  a  solution  of  potassium 


dihydrogen  phosphate  with  ammonium  molybdate  solution  in  the 
presence  of  ammonium  nitrate,  washing  with  1  %  nitric  acid  solution, 
dissolving  the  precipitate  in  ammonium  hydroxide  and  reprecipitat- 
ing  with  nitric,  hydrochloric  or  sulphuric  acid  three  times.  The 
precipitates  after  the  first  were  washed  with  the  corresponding  acid 
and  finally  twice  with  cold  water  and  then  dried. 

Washing  solution. 

The  washing  solution  found  most  satisfactory  for  washing  the 
yellow  phosphomolybdate  precipitate  contained  10  grams  of  ammo- 
nium nitrate  and  5  cc.  of  concentrated  nitric  acid  per  liter  of  solu- 
tion. 

Magnesia  Mixture. 

In  order  that  both  phosphorus  and  molybdenum  could  be  deter- 
mined in  the  same  solution  it  was  necessary  to  avoid  the  presence  of 
chloride  in  the  magnesia  mixture.  This  reagent  was  therefore  pre- 
pared containing  acetates  and  an  amount  of  magnesium  equivalent 
to  that  contained  in  the  magnesia  mixture  ordinarily  used.  For  the 
preparation  of  this  reagent  5.5  grams  of  magnesium  oxide  were  dis- 
solved in  a  slight  excess  of  acetic  acid  solution.  To  this  solution 
ammonium  acetate  was  added  in  sufficient  quantity  to  prevent  the 
subsequent  precipitation  of  magnesium  in  the  alkaline  solution  finally 
obtained.  The  solution  was  then  neutralized  with  ammonia  and  an 
excess  equivalent  to  25  cc.  of  concentrated  ammonia  was  added. 
The  volume  of  the  solution  was  now  brought  up  to  500  cc.  by  the 
addition  of  water. 

Lead  acetate  solution. 

For  the  precipitation  of  molybdenum  as  lead  molybdate,  a  lead 
acetate  solution  was  prepared  by  dissolving  20  grams  of  lead  acetate 
in  500  cc.  of  water  and  adding  sufficient  acetic  acid  to  prevent 
hydrolysis. 

COMPOSITION  OF  THE  AMMONIUM  PHOSPHOMOLYB- 
DATE PRECIPITATE 

(a)  The  Molecular  ratio  of  phosphorus  pent  oxide  to  molybdic  oxide. 
Method  of  Procedure :  The  yellow  precipitate,  prepared  as  de- 
scribed above,  was  analysed  by  precipitating  the  phosphorus  with 
the  magnesium  acetate  solution  and  the  molybdenum  in  the  filtrate 
with  lead  acetate.  The  method  was  first  tested  by  mixing  known 


—10— 

weights  of  potassium  dihydrogen  phosphate  and  molybdic  oxide 
approximately  in  the  proportion  found  in  the  yellow  precipitate. 

The  molybdic  oxide  was  dissolved  in  ammonium  hydroxide,  the 
potassium  dihydrogen  phosphate  added,  the  solution  made  slightly 
acid  with  acetic  acid  and  magnesium  acetate  solution  added.  10  cc. 
of  the  latter  were  used  for  20  to  25  mg.  of  phosphorus  and  the 
volume  of  the  resulting  solution  made  about  250  cc.  This  was 
heated  to  about  70°C,  ammonium  hydroxide  added  slowly  with 
constant  stirring  until  the  solution  was  alkaline,  and  then  5  cc.  of 
concentrated  ammonium  hydroxide  added  in  excess.  After  standing 
six  hours  or  longer  the  precipitate  was  filtered  off,  the  filtrate  and 
washing  solution  being  caught  in  volumetric  flask  which  had  pre- 
viously been  calibrated.  The  precipitate  was  washed  with  \% 
ammonium  hydroxide  solution  and  then  dissolved  in  10  to  20  cc. 
of  6M  HC1  solution.  To  this  solution  2  cc.  of  magnesium  acetate 
solution  were  added  and  the  magnesium  ammonium  phosphate  re- 
precipitated  as  above  described  by  adding  ammonium  hydroxide 
slowly  and  with  constant  stirring.  Sometimes  the  precipitate  when 
first  formed  was  gelatinous  but  it  changed  over  within  a  short  time 
into  the  crystalline  form.  After  standing  it  was  filtered  on  a  proce- 
lain  Gooch  crucible,  washed  free  of  chlorides,  ignited  to  constant 
weight  and  weighed  as  magnesium  pyrophosphate.  By  drying  the 
precipitate  in  the  crucible  slowly  on  a  quartz  plate  over  a  burner, 
igniting  slowly  by  means  of  a  Bunsen  burner  and  finally  with  a 
Meker  burner  a'  residue  was  obtained  which  was  light  gray.  In 
very  few  cases  only  was  the  residue  pure  white. 

The  filtrate  from  the  first  precipitation  was  made  up  to  a  defi- 
nite volume  at  25  °C.  and  portions  weighed  out  by  means  of  a  weight 
burette.  The  density  of  the  solution  was  determined  at  25  °C.  Thus 
the  volume  of  the  portion  taken  for  analysis  could  be  calculated. 
This  portion  was  taken  of  such  a  size  as  not  to  give  more  than  0.25 
grams  of  precipitate.  It  was  made  slightly  acid  with  acetic  acid, 
10  cc.  of  an  ammonium  nitrate  solution  containing  5  grams  of  the 
salt  were  added,  and  the  whole  diluted  to  300  cc.  The  solution  was 
then  heated  almost  to  the  boiling  point  and  10  cc.  of  lead  acetate 
solution  added  slowly  with  stirring.  After  standing  twelve  hours 
the  precipitate  was  filtered  on  paper,  washed  with  hot  water,  ignited 
gently  with  the  Bunsen  flame  in  a  porcelain  crucible  and  weighed  as 
PbMoO4.  It  was  found  necessary  to  add  ammonium  nitrate  to  the 
solution  in  order  to  form  a  precipitate  of  such  character  that  it  could 
be  filtered.  The  following  results  were  obtained : 


—11— 

P  calculated              P  calculated            Weight  Mo03  Mo03  found  from 

fromKH2P04          fromMg2P2O7                    used  PbMoO4 

. 01634  g.                     . 01622  g.                     0.8348g.  0.8349g. 

.03910                         .03941                         1.6124  1.6125 

.03233                         .03264                         1.8045  1.8059 

.02389                         .02394                         1.9520  1.9501 

.02487                        .02475                        0.9698  0.9709 

The  average  deviation  of  the  weight  of    P  found  from    the 

weight  used  is  6  parts  per  1000.    The  values  found  for  MoO3  check 

those  used  within  1  part  per  1000. 

Experimental  Data 

Portions  of  precipitates  prepared  as  described  above  were 
weighed  out,  dissolved  io  ammonium  hydroxide  and  analysed  by  the 
above  method.  In  each  case  the  analysis  was  made  on  a  different 
phosphomolybdate  precipitate. 

Acid  used  for  Method  of  treat-  Ratio 

reprecipitation  ing  precipitate  P20g       MoO3     P2O5:MoO3 

HNO3  dried  with  alcohol  and  ether,     3.56%     87.63       '    1:24.25 

then  at  110°  for  10  min.          3 . 56        87 . 33  1 :24.16 

HC1  dried  with  alcohol  and  ether,     3.47         85.20  1:24.22 

then  at  110°  for  10  min.          3.58        88.02  1:24.23 

H2SO4  dried  with  alcohol  and  ether,     3 . 50         86 . 02  1 : 24.25 

then  at  110°  for  10  min.          3.51        86.11  1:24.20 

HNO3  dried  at  110°C.  for  2  hrs.         3.67         89.84  1:24.16 

3.69         90.57  1:24.20 

3.73        92.05  1:24.34 

3.73        92.30          1:24.38 

HNO3  dried    over    H2SO4    in    the      3.72        91.17  1:24.16 

dark,  to  constant  weight        3 . 74        91 . 28  1 : 24.09 

Mean  molecular  ratio. . . .     1:24.22 

Although  the  actual  percentages  found  do  not  agree  it  is  seen 
that  the  ratio  of  phosphorus  pentoxide  to  molybdic  oxide  is  con- 
stant, whether  the  precipitate  is  dried  at  110°C.,  with  alcohol  and 
ether,  or  over  H2SO4,  and  whether  formed  in  the  presence  of  nitric, 
hydrochloric  or  sulphuric  acid.  The  average  deviation  of  the  above 
ratios  is  2.5  parts  per  1000.  The  variation  in  composition  is  there- 
fore due  to  variation  in  the  amount  of  other  constituents  in  the 
molecules,  as  for  instance  ammonia  and  water,  due  to  the  method 
of  preparing  the  precipitate  for  weighing.  In  most  cases  where  the 
precipitate  was  dried  at  110°C.  the  ammoniacal  solution  was  slightly 
blue  showing  reduction  of  molybdenum  to  a  small  extent. 

The  molecular  ratio  of  phosphorus  pentoxide  to  molybdic  oxide 
was  found  when  a  given  weight  of  phosphorus  was  precipitated  and 
the  precipitate  obtained  was  analysed. 


—12— 
Method  of  Procedure: 

A  number  of  precipitates  formed  under  varying  conditions 
were  dried  at  110°  and  analysed. 

1.  To  a  volume  of  150  cc.  containing  about  47  mg.  of  phos- 
phorus pentoxide,  10  cc.  of  concentrated  sulphuric  acid  and  30 
grams  of  ammonium  nitrate  were  added.  The  solution  was  heated 
to  75°  and  40  cc.  of  molybdate  solution  (20  cc.  of  the  above 
described  ammonium  molybdate  solution  poured  into  20  cc.  of  8M 
nitric  acid)  added.  After  standing  over  night,  the  precipitate  was 
filtered  off,  washed  with  the  ammonium  nitrate,  nitric  acid  solution, 
dissolved  in  ammonium  hydroxide  and  reprecipitated  from  a  hot 
solution  with  nitric  acid  after  adding  2  cc.  of  the  molybdate  solu- 
tion. After  standing  the  precipitate  was  filtered  on  a  porcelain 
Gooch,  washed  with  the  ammonium  nitrate,  nitric  acid  solution 
five  to  six  times,  then  twice  with  \%  nitric  acid  solution  and  dried 
to  constant  weight  at  110°C.  This  precipitate  was  dissolved  and 
analysed  as  described  above. 

2.  Same  as  1  except  that  the  molybdate  solution  contained  10 
grams  of  the  salt  in  100  cc.  of  water.    Also  the  first  precipitate  was 
filtered  on  a  Gooch,  finally  washed  twice  with  ice  cold  water,  dried 
at  110°  and  weighed.     This  precipitate  was  then  dissolved  and  re- 
precipitated  with  nitric  acid  adding  2  cc.  of  the  ammonium  molyb- 
date solution,  filtered  on  a  Gooch,  washed  with  the  ammonium  ni- 
trate, nitric  acid  solution,  finally  twice  with  ice  cold  water,  dried 
at  110°C.  and  weighed.     This  precipitate  was  dissolved  and  ana- 
lysed. 

3.  Same  as  2  except  that  the  first  precipitate  was  dissolved  and 
analysed. 

4.  In  a  volume  of  40  cc.  containing  about  47  mg.  of  phosphorus 
pentoxide  and  5  grams  of  ammonium  nitrate  the  phosphorus  was 
precipitated  in  the  cold  with  60  cc.  of  ammonium  molybdate  solution 
(20  cc.  of  the  above  described  solution  I  poured  into  40  cc.  of  solu- 
tion II).     After  standing    12    hours    the    precipitate  was  filtered, 
washed  with  the  ammonium  nitrate,  nitric  acid  solution,  then  twice 
with  \%  nitric  acid  solution,  dried  at  110°  and  weighed.    This  was 
dissolved,  reprecipitated  with  nitric  acid,  washed,  dried  and  weighed 
as  before.    This  precipitate  was  dissolved  and  analysed. 

5.  Same  as  4  except  that  the  first  precipitate  was  dissolved  and 
analysed. 

6.  Same  as  4  except  that  5  grams  of  ammonium  chloride  were 
used  in  place  of  ammonium  nitrate  and  hydrochloric  acid  in  place 


—13— 

of  nitric.  After  standing  the  precipitate  was  filtered,  washed  with 
an  ammonium  chloride  solution,  then  twice  with  \%  hydrochloric 
acid  solution.  After  drying  at  110°  it  was  dissolved  and  reprecipi- 
tated  with  nitric  acid.  This  precipitate  was  treated  as  in  4  then 
dssolved  and  analysed. 

7.  Same  as  6  except  that  the  first  precpitate  was  dissolved  and 
analysed. 

Experimental  Data 
Wt.  of  yellow 


Exp. 

Method 

ppt.  per  47  mg.  of 

P2°5 

P205  taken 

1 

1 

1.2755g. 

3.56% 

2 

1 

1.2850 

3.55 

3 

2 

1.2718 

3.63 

4 

3 

1.2930 

3.59 

5 

3 

1.2383 

3.56 

6 

4 

1.1693 

3.62 

7 

5 

1.2583 

3.60 

8 

6 

1.2152 

3.62 

9 

7 

1.2390 

3.60 

Mo0 


Ratio 
).:Mo03 
1:25.37 
1:25.47 
1:24.95 
1:25.17 
1:25.46 
1:25.19 
1:25.36 
1:25.12 
1:25.32 
1:25.27 


91.60% 
91.57 
91.74 
91.65 
91.82 
92.52 
92.51 
92.25 
92.49 
Mean  molecular  ratio 

The  above  results  were  obtained  by  starting  with  definite  known 
weights  of  phosphorus  pentoxide.  The  yellow  precipitate  formed  in 
each  case  was  dried  at  110*  and  weighed  before  analysing.  The 
wide  variation  in  the  weight  of  ammonium  phosphomolybdate  pre- 
cipitate obtained  from  a  given  weight  of  phosphorus  arises  either  in 
a  variable  decomposition  of  the  precipitate  during  drying  or  in  the 
difference  in  the  conditions  of  precipitation.  In  all  cases  the  surface 
of  the  dried  precipitates  were  greenish  and  the  ammoniacal  solutions 
were  blue.  The  intensity  of  the  blue  color  varied. 

The  conditions  of  precipitation  described  except  in  the  case  of 
experiments  8  and  9  are  similar  to  conditions  of  precipitation  found 
in  the  literature.  In  experiments  8  and  9  chloride  ion  was  intro- 
duced. In  experiments  1,  2,  3,  6  and  8  the  precipitate  obtained  upon 
reprecipitation  was  the  one  which  was  analysed^  while  in  experi- 
ments 4,  5,  7  and  9  the  original  precipitate  was  analysed.  Upon 
comparing  the  molecular  ratio  of  phosphorus  pentoxide  to  molybdic 
oxide  it  will  be  noticed  that  there  is  no  difference  obtained  whether 
the  first  or  second  precipitate  is  analysed.  For  instance,  in  experi- 
ment 1  the  ratio  is  1 : 25.37  while  in  7  it  is  1 : 25.36  and  in  experi- 
ment 4  the  ratio  is  1 : 25.17  while  in  experiment  6  it  is  1 : 25.19. 
Reprecipitation,  therefore,  does  not  appear  to  effect  the  composition 
of  the  precipitate. 


—14— 

It  will  also  be  noticed  that  although  the  percentages  of  phos- 
phorus pentoxide  in  the  yellow  phosphomolybdate  precipitates  found 
are  fairly  constant,  the  precipitates  vary  in  molybdenum  content. 
The  average  deviation  of  these  ratios,  namely  5.6  parts  per  1000,  is 
larger  than  that  found  in  the  case  of  the  previous  precipitates  formed 
by  precipitating  large  amounts  of  phosphorus  and  analysing  portions 
of  the  precipitates  obtained.  This  second  set  of  precipitates  ob- 
tained from  known  weights  of  phosphorus  and  the  whole  precipitate 
analysed  are  higher  in  molybdenum  content  than  the  first.  It  was 
thought  that  this  might  be  due  to  molybdenum  occluded  on  the  above 
precipitates.  In  preparing  large  quantities  no  molybdate  solution 
was  added  before  successive  reprecipitations,  while  in  precipitating 
the  phosphorus  from  a  known  weight  of  potassium  dihydrogen 
phosphate,  2  cc.  of  molybdate  solution  were  added  before  precipi- 
tation. 

An  experiment  was  therefore  tried  where  the  phosphorus  was 
precipitated  according  to  method  4  above  except  that  on  reprecipi- 
tation  no  molybdate  was  added.  The  following  results  were  ob- 
tained: 3.73%  P2O5,  92.34%  MoO3,  ratio  P2O5:MoO3  1:24.41. 
This  ratio  checks  the  first  set  obtained.  From  this  it  is  evident 
that  the  precipitates  obtained  according  to  the  above  7  methods 
contained  more  molybdenum  than  the  other  precipitates.  If  this 
excess  of  molybdenum  is  constant,  however,  no  error  would  be 
introduced  in  a  determination  of  phosphorus  depending  on  the 
composition  of  the  ammonium  phosphomolybdate  precipitate.  The 
conditions  for  obtaining  a  precipitate  of  constant  composition  will 
be  discussed  later. 

(b)The  Presence  of  acid  in  the  Molecule. 

A  great  variety  of  formulas  have  been  proposed  for  the  yellow 
phosphomolybdate  precipitate,  some  of  which  are 
(NH4)3PO4  .  10MoO3,  (NH4)3PO4  .  10MoO3  .  14H2O,  (NH4)3 
PO4  .  llMoO8,  (NH4)3PO4  .  HMoO3  .  12H2O,  (NH4)3PO4  . 
12MoO3,  (NH4)3PO4  .  12MoO3  .  3H2O,  (NH4)3PO4  .  12MoO3 
+  (NH4)2HPO4  .  12MoO3+8H2O,  (NH4)2'HPO4  .  12MoO3, 
(NH4)3PO4  .  12.65MoO3,  (NH4)3PO4  .  12.75MoO3,  (NH4)3PO4  . 
12MoO3  .  2HNO3  .  H2O,  4[(NH4)3PO4  .  12MoO3]  +  (NH4)2SO4 . 
5Mo03,  8(NH4)3P04  .  12Mo03+ (NH4)2S04  .  8MoO3.  The  last 
two  formulas  are  given  for  precipitates  formed  in  solutions  contain- 
ing large  amounts  of  sulphate  ion. 


-15- 

Hundeshagen    (Z.  f.  Anal.  Chem.  28,  141  (1889),  Neumann 
(Z.  Physiol.  Chem.  37,  115    1903),  Richardson  (J.A.C.S..  29,  1314 
(1907),  Artmann  and  Brandis    (Z.  f.  Anal.  Chem.  49,  1   (1910), 
Falk    and    Sugiura     (J.A.C.S.  37,  1507    (1915)    and  Posternak 
(Compt.  Rend.  170,  930  (1920)  consider  that  the  phosphomolyb- 
date  (NH4)3PO4  .  12MoO3  combines  in  various  ways  with  the  acids 
or  salts  present  in  the  solution  to  form  further  complexes  containing 
nitric  acid,  sulphuric  acid  or  sulphomolybdates.       The  arguments 
advanced  by  these  authors  for  the  formulas  which  they  propose  are 
as  follows : 

Hundeshagen  states  that  the  precipitate  obtained  with  excess 
acid,  washed  with  cold  dilute  acid  and  dried  in  a  desiccator  contains 
two  molecules  of  acid  with  one  molecule  of  water  probably  in  un- 
stable chemical  combination.  Both  acid  and  water  are  expelled 
completely  at  a  temperature  exceeding  130°C.  for  on  heating  the 
precipitate  to  this  temperature  it  lost  weight  giving  off  moist 
strongly  acid  vapors.  In  the  case  of  the  nitric  acid  compound  the 
loss  in  weight  was  7.13%  or  7.67%  on  the  substance  dried  at  150°, 
the  hydrochloric  acid  compound  4.78%  or  5.02%  on  the  substance 
dried  at  150°C.  The  precipitates  dried  in  a  desiccator  required  for 
neutralization  two  equivalents  more  alkali  than  those  dried  at  150° 
corresponding  to  as  many  equivalents  of  nitric  or  hydrochloric  acid 
in  combination  with  the  phosphomolybdate.  In  point  of  weight 
two  molecules  of  nitric  acid  would  amount  to  6.71%  and  two  mole- 
cules of  hydrochloric  acid  to  3.89%  if  referred  to  phosphomolybdate 
free  from  acid  and  water.  If  the  numbers  found  as  loss  of  weight 
on  heating  to  150°  the  salts  previously  dried  in  a  desiccator  are 
diminished  by  these  amounts  there  remain  for  water  0.96%  and 
1.13%,  of  which  figures  the  former  represents  exactly  and  the  latter 
approximately  a  molecule  of  water.  From  these  facts  he  writes  the 
formula  of  the  phosphomolybdate  precipitate  (NH4)3PO4  .  12MoO3  . 
2HNO3  .  H2O  or  (NH4)3PO4  .  12MoO3  .  2HC1  .  H2O  when 
formed  in  a  solution  containing  chlorides. 

Neumann  accepts  Hundeshagen's  formula  for  the  ammonium 
phosphomolybdate  precipitate.  The  latter  has  shown  that  the  two 
molecules  of  nitric  acid  can  easily  be  replaced  by  salts  or  other 
acids  present  in  solution.  Neumann  determined  phosphorus  in 
organic  matter.  Since  in  ashing  sulphuric  and  nitric  acids  were 
present  and  a  large  amount  of  ammonium  nitrate  was  added  to 
insure  complete  precipitation,  he  believes  that  there  can  easily  be  a 
change  in  that  part  of  the  molecule.  Such  changes  in  composition, 


—16— 

however,  he  found  have  no  effect  on  the  amount  of  sodium  hy- 
droxide required  for  titration. 

Richardson  found  that  in  the  presence  of  sulphates,  sulphuric 
acid  or  a  sulphate  was  always  found  by  analysis  in  the  yellow 
phosphomolybdate  precipitate.  He  states  that  it  is  altogether  pro- 
bable that  a  complex  ammonium  sulphomolybdate  is  formed  which 
has  the  acid  nature  of  ammonium  phosphomolybdate  and  therefore 
reacts  with  alkali  similarly  to  the  latter. 

Artmann  and  Brandis  performed  two  experiments  to  show  the 
effect  of  sulphate  on  the  ammonium  phosphomolybdate  precipitate. 
In  the  first  the  phosphorus  was  precipitated  in  the  presence  of  am- 
monium nitrate  and  potassium  sulphate  at  40° C,  in  the  second  in 
the  presence  of  ammonium  sulphate.  In  both  cases  the  precipitates 
were  dissolved,  the  ammonia  distilled  off  and  titrated,  with  high 
results.  After  acidifying  the  residues  with  nitric  acid  and  adding 
barium  chloride,  precipitates  of  barium  sulphate  were  obtained. 

Falk  and  Siguira  precipitated  phosphorus  as  ammonium  phos- 
phomolybdate in  the  presence  of  sulphuric  acid  according  to  Neu- 
mann. They  found  that  the  precipitate  thus  formed  contained 
sulphate  as  an  essential  part  of  the  molecule  together  with  excess 
molybdic  oxide  and  no  nitric  acid.  They  found  that  the  titration 
values  were  the  same  whether  or  not  the  precipitate  was  dried  at 
120°  thus  showing  that  no  nitric  acid  was  contained  in  the  precipi- 
tate formed  in  a  solution  containing  sulphuric  acid  and  ammonium 
nitrate.  They  determined  the  amount  of  sulphate  in  the  precipitate 
by  dissolving  it  in  ammonium  hydroxide,  reprecipitating  with  nitric 
acid,  filtering,  evaporating  the  filtrate  to  dryness  after  adding  hydro- 
chloric acid,  taking  up  the  residue  with  water,  filtering  and  adding 
barium  chloride  to  the  filtrate.  They  thus  obtained  .0179  -  .0214 
grams  of  barium  sulphate  from  precipitates  from  phospate  solu- 
tions containing  47.1  mg .  P2O5.  Similar  treatment  of  a  corre- 
sponding solution  without  sulphuric  acid  gave  .0001  and  .0004  grams 
of  barium  sulphate. 

Posternak  prepared  ammonium  phosphomolybdate  under  vary- 
ing conditions  and  analysed  the  precipitates  for  phosphorus,  in  some 
cases  transforming  them  into  the  barium  salts.  He  found  that 
phosphoric  acid  fixes  12,  sulphuric  acid  8  and  nitric  acid  4  mole- 
cules of  molybdic  oxide  and  concludes  that  in  acid  solution  a  tetra- 
molybdate  is  present  which  can  combine  with  all  mineral  acids 
present  in  solution. 


—17— 

Other  investigators  do  not  agree  with  the  above  authors  re- 
garding the  presence  of  acid  or  sulphate  in  the  molecule  of  ammo- 
nium phosphomolybdate.  Blair  and  Whitfield  (J.A.C.S.  17,  747 
(1895)  found  that  the  amount  of  alkali  required  to  titrate  a  pre- 
cipitate when  washed  with  water  or  dilute  acid  and  dried  over  potas- 
sium hydroxide  for  three  months  was  less  than  that  required  to 
titrate  a  precipitate  which  was  dried  at  150°C.  from  which,  accord- 
ing to  Hundeshagen,  the  acid  would  be  removed.  Further  Frese- 
nius  (Z.  f.  Anal.  Chem.  3,  446  (1864)  and  Richters  (Z.  f.  Anal. 
Chem.  10,  469  (1871)  found  that  sulphuric  acid  does  not  interfere 
with  precipitation  of  ammonium  phosphomolybdate. 

The  work  of  the  present  investigation  shows  that  the  presence 
of  sulphuric  acid  or  hydrochloric  acid  in  solution  has  no  effect  on 
the  precipitation  of  phosphorus  as  ammonium  phosphomolybdate 
and  that  neither  sulphate  nor  chloride  is  contained  in  the  molecule 
under  the  conditions  herein  adopted. 
Method  of  Procedure: 

The  presence  of  sulphate  was  tested  for  in  precipitates  obtained 
as  follows :  Enough  potassium  dihydrogen  phosphate  was  weighed 
out  to  furnish  from  46  to  68  mg.  of  P2O5.  This  was  dissolved  in 
water,  10  grams  of  ammonium  nitrate  added  in  solution,  and  diluted 
to  140  cc.  To  this  cold  solution  were  added  45  cc.  ammonium  molyb- 
date  solution,  (15  cc.  of  the  ammonium  molybdate  solution  I  poured 
into  30  cc.  6MH2SO4)  and  the  solution  stirred  for  a  few  minutes. 
The  precipitate  does  not  form  as  rapidly  as  in  a  nitric  acid  solution 
and  tends  to  stick  on  the  beaker.  After  standing  over  night  the  pre- 
cipitate was  filtered  off  and  washed  with  the  ammonium  nitrate, 
nitric  acid  solution.  After  washing  carefully  with  about  400  cc.  of 
wash  solution,  the  funnel  being  allowed  to  drain  between  washings, 
it  was  still  possible  to  obtain  a  test  for  sulphate  by  adding  barium 
chloride  to  a  small  amount  of  washings  and  shaking  for  a  few  min- 
utes. The  yellow  precipitate  was  then  dissolved  in  10  cc.  of  con- 
centrated ammonium  hydroxide,  2  cc.  of  molybdate  solution  added 
and  reprecipitated  by  adding  nitric  acid.  After  standing  again  this 
precipitate  was  filtered  off,  washed  with  the  same  solution  as  above, 
and  the  filtrate  plus  washings  evaporated  to  dryness  adding  5  cc. 
concentrated  hydrochloric  acid  when  the  solution  was  almost  dry. 
The  residue  was  taken  up  with  dilute  hydrochloric  acid,  the  molyb- 
denum compound  which  separated  filtered  off,  and  5  cc.  of  m/4 
barium  chloride  solution  added.  After  standing  24  hours  the  result- 
ing barium  sulphate  was  filtered  off  and  weighed.  Blank  deter- 


—18— 

minations  were  made  in  a  similar  manner  on  precipitates  obtained 
from  solutions  containing  nitric  acid  in  place  of  sulphuric  acid. 


Experimental  results 


P205  cal- 
culated 
from 
KH2P04 


BaSO,       Wtof  BaSOx 


P2O5  calcu- 


BaSO 


gms.         per  50  mg.        lated  from       gins. 


KH2P04 


.0468g. 
.0474 

.0136 
.0111 

.0145g. 
.0117 

.0536g. 
.0543 

.0199g. 
.0040 

.0480 

.0234 

.0244 

.0557 

.0246 

.0484 

.0242 

.0250 

.0574 

.0154 

.0516 

.0155 

.0150 

.0578 

.0158 

.0526 

.0054 

.0051 

.0624 

.0122 

.0534 

.0108 

.0101 

.0810 

.0264 

Wt.  of  BaSO4 
per  50  mg.  of 

P2°5 

.0186g. 

.0037 

.0221 

.0134 

.0137 

.0098 

.0163 

Blank  Determinations 

.0534  .0047  .0044 

.0641  .0042  .0033 

.0646  .0033  .0026 

It  will  be  seen  that  the  blanks  are  much  higher  than  those  given 
by  Falk  and  Sigiura.  It  is  very  probable  that  all  the  barium  sulphate 
precipitates  were  obtained  from  sulphate  which  had  not  been  washed 
out.  The  irregularity  of  results  can  certainly  be  explained  by  assum- 
ing the  presence  of  varying  amounts  of  sulphate  left  in  or  adsorbed 
upon  the  precipitate,  for,  as  stated  above,  it  seemed  impossible  to 
wash  the  precipitate  free  of  sulphate.  From  these  facts  the  con- 
clusion was  drawn  that  sulphate  is  not  a  part  of  the  ammonium 
phosphomolybdate  molecule  when  it  is  formed  in  a  solution  con- 
taining sulphate. 

The  presence  of  molybdenum  was  tested  for  in  some  of  the 
above  barium  sulphate  precipitates  by  fusing  with  sodium  carbonate, 
dissolving  in  hydrochloric  acid  and  passing  hydrogen  sulphide  into 
the  solution.  A  brown  precipitate  of  molybdenum  sulphide  was 
obtained. 

A  few  experiments  were  performed  to  test  for  the  presence  of 
hydrochloric  acid  in  the  molecule  of  the  precipitate  formed  in  a 
chloride  solution.  Known  weights  of  potassium  dihydrogen  phos- 
phate were  dissolved  in  water,  5  grams  of  ammonium  chloride  added 
and  the  whole  diluted  to  about  120  cc.  To  this  cold  solution  were 
added  45  cc.  of  molybdate  solution  (15  cc.  of  the  ammonium  molyb- 
date  solution  poured  into  30  cc.  of  dilute  hydrochloric  acid  containing 
12  cc.  of  concentrated  acid  and  18  cc.  of  water)  and  the  solution 
stirred.  After  standing  12  hours,  the  precipitate  was  filtered  ofif 


—19— 

and  washed  with  the  ammonium  nitrate,  nitric  acid  solution.  The 
precipitate  was  dissolved  in  ammonium  hydroxide  and  reprecipi- 
tated  by  adding  2  cc.  of  molybdate  solution  and  15  cc.  of  concen- 
trated nitric  acid.  The  filtrate  from  the  second  precipitation  was 
evaporated  to  a  pasty  mass,  to  avoid  losing  any  hydrochloric  acid 
which  might  be  present,  taken  up  with  dilute  nitric  acid,  filtered  and 
silver  nitrate  added  to  the  filtrate.  Of  four  tested  qualitatively,  two 
gave  precipitates  and  two  none.  Of  the  two  which  gave  precipitates 
neither  was  as  large  as  the  blank.  Another  precipitate  obtained  by 
adding  silver  nitrate  stood  in  the  light  for  several  weeks  without 
showing  any  discoloration.  The  precipitates  obtained  were  un- 
doubtedly not  silver  chloride  and  probably  contained  molybdenum 
from  the  excess  molybdate  solution  added  in  reprecipitation  of  the 
yellow  precipitate  which  is  shown  by  the  large  blank  obtained. 

A  number  of  authors  consider  that  either  the  nitric  acid  or  the 
ammonium  radical  in  ammonium  phosphomolybdate  or  both  are 
held  in  such  unstable  combination  as  to  be  readily  replaced  by  vari- 
ous ions  used  in  washing  solutions. 

Artmann  (Z.  angew.  Chem.  26,  Aufstatzteil  203  (1913)  agrees 
with  Hundeshagen  that  the  two  molecules  of  nitric  acid  in  the  mole- 
cule of  ammonium  phosphomolybdate  can  be  replaced  by  two 
molecules  of  ammonium  nitrate  when  washing  with  a  neutral  solu- 
tion of  that  salt. 

Baxter  and  Griffin  (A.  Chem.  Jour.  34,  204  (1905)  found  that 
the  ammonium  was  replaced  by  potassium.  In  determining  ammo- 
nia, in  order  to  decide  whether  molybdic  oxide  or  ammonium 
molybdate  was  occluded  on  the  ammonium  phosphomolybdate  pre- 
cipitate, they  washed  the  precipitate  with  potassium  nitrate  solution. 
They  state  "it  was  evident  that  either  ammonium  phosphomolybdae 
contains  very  much  less  ammonium  than  was  usually  supposed,  or 
else  the  ammonium  in  the  precepitate  had  been  replaced  by  potas- 
sium of  the  washing  solution.  The  latter  explanation  proved  to  be 
the  correct  one."  Still  the  authors  give  the  formula  for  the  pre- 
cipitate as  (NH4)2HPO4  .  12MoO3,  only  two  hydrogens  of  phos- 
phoric acid  replaced  by  ammonium,  and  also  decide  that  ammonium 
molybdate  is  occluded.  The  authors  believe  that  the  third  hydrogen 
is  replaced  upon  heating  the  yellow  precipitate  to  300°C.  by  ammo- 
nium from  the  ammonium  nitrate  which  remains  on  the  precipitate 
after  washing  with  ammonium  nitrate  solution. 

This  matter  was  not  considered  worthy  of  investigation  in  the 
present  research  because  since  we  are  dealing  with  a  crystalline  pre- 


—20— 

cipitate  such  replacement,  if  it  occurs  at  all,  can  occur  only  upon 
the  surface  of  the  crystal  particles  and  is  therefore  without  signi- 
ficance in  a  determination  of  the  composition  of  the  yellow  precipi- 
tate. In  view  of  the  negative  results  of  the  experiments  conducted 
in  this  research  seeking  to  produce  phosphomolybdates  containing 
hydrochloric  or  sulphuric  acid  under  the  most  favorable  conditions 
for  their  formation  it  is  not  thought  that  the  reactions  claimed  by 
Hundeshagen,  Artmann,  and  Baxter  and  Griffin  occur  even  at  the 
surface  of  the  precipitated  phosphomolybdate. 

NEW  METHOD  FOR  THE  PRECIPITATION  OF 
AMMONIUM  PHOSPHOMOLYBDATE 

The  factors  which  must  be  considered  in  determining  the  con- 
ditions for  complete  precipitation  of  phosphorus  and  at  the  same 
time  obtaining  a  precipitate  of  constant  composition  are,  (1)  the 
molybdate  solution,  (2)  the  temperature  of  precipitation,  (3)  the 
volume  and  acidity  of  the  solution  before  precipitation,  (4)  washing 
of  precipitate.  Some  authors  also  believe  that  the  rapidity  with 
which  the  precipitating  solution  is  added  has  an  effect  on  the  com- 
position of  the  precipitate  and  also  the  length  of  time  the  precipitate 
is  allowed  to  stand  before  filtering. 

Molybdate  solutions  in  great  variety  have  been  proposed. 
Those  which  have  been  tested  in  this  investigation  have  been  found 
unsatisfactory  largely  because  of  their  instability  or  erratic  be- 
havior in  the  precipitation  of  ammonium  phosphomolybdate.  In 
order  to  overcome  these  defects  in  the  reagents  a  radical  change  has 
been  made  in  its  preparation.  By  preparing  this  reagent  in  two 
solutions  as  above  described,  it  is  perfectly  stable  and  its  use  in  the 
manner  described  leads  to  definite  and  consistent  results.  Further 
it  is  sufficiently  sensitive  to  low  concentrations  of  phosphate  ion  to 
admit  of  precipitation  in  cold  solution  as  a  general  procedure.  How- 
ever in  the  determination  of  phosphorus  in  steel,  the  abnormally 
high  concentration  of  ferric  ion  interferes  with  the  precipitation  of 
the  phosphomolybdate  probably  due  to  the  formation  of  complexes 
of  ferric  ion  and  phosphate.  In  this  case  therefore  it  is  necessary 
to  heat  the  mixture  to  60° C.  and  agitate  by  shaking  for  a  few 
minutes  under  which  conditions  the  precipitate  readily  forms. 

The  recommendations  in  the  literature  as  to  the  temperature  at 
which  the  precipitation  of  ammoinum  phosphomolybdate  is  to  be 
carried  out  are  as  varied  as  are  those  concerning  the  other  condi- 
tions of  the  procedure.  Woy  (Chem.  Ztg.  21,  441  (1897)  and 


—21— 

also  Kleinmann  '  (Biochem.  Zeitschr.  99,  19  (1919)  precipitate  at 
boiling  temperature,  Kilgore  (J.A.C.S.  16,  765  (1894);  17,  950 
(1895)  at  60°,  Wood*  (J.  Anal,  Chem.  1,  138  (1887)  at  30-40°, 
Meineke  (Chem.  Ztg.  20,  108  (1896)  at  50-60°,  Gladding  (J.A. 
C.S.  18,  23  (1896),  also  Jorgensen  (Z.  f.  Anal.  Chem.  46,  370 
(1907)  at  50°,  Chesneau  (Compt.  Rend.  146,  758  (1908)  precipi- 
tates at  65-70°  to  avoid  the  formation  of  ammonium  tetramolyb- 
date.  Artmann  and  Brandis  (Z.  f.  Anal.  Chem.  49  f  1,  (1910)  use 
50  cc.  of  solution,  precipitate  at  40-50°,  a  higher  temperature  caus- 
ing adsorption  of  molybdenum  as  ammonium  tetramolybdate.  Hib- 
bard-  (J.  Ind,  Eng.  Chem.  5,  998  (1913)  uses  65°  to  prevent  the 
separation  of  molybdic  acid. 

Artmann  and  Brandis  believe  that  the  rapidity  with  which 
the  molybdate  solution  is  added  has  a  large  influence.  They  add  the 
solution  dropwise.  Gladding  makes  a  point  of  adding  the  solution 
slowly  and  stirring.  Rapid  addition  causes  adsorption  of  molybdic 
acid.  Artmann  and  Brandis  also  allow  the  precipitate  to  stand  in 
contact  with  the  solution  for  an  hour  and  a  quarter  only  at  40°,  not 
longer,  in  order  to  avoid  adsorption  of  molybdenum. 

Washing:  Gladding  washes  with  \%  nitric  acid  solution  then 
water.  Chesneau,  Woy,  Jorgensen,  and  Christensen  (Z.  f.  Anal. 
Chem.  47,  529  (1908)  use  an  ammonium  nitrate,  nitric  acid  solution. 
Chesneau  also  uses  water.  Isbert  and  Stutzer  (Z.  f.  Anal.  Chem. 
26,  583  (1887)  wash  with  ice  cold  water.  Artmann  and  Brandis 
observed  turbidity  after  washing  with  water  which  they  claim  was 
white  ammonium  tetramolybdate  and  contained  no  phosphorus. 

In  the  present  investigation  the  most  satisfactory  wash  solution 
was  found  to  be  one  containing  10  grams  of  ammonium  nitrate  and 
5  cc.  of  concentrated  nitric  acid  per  liter.  A  1  %  nitric  acid  solution 
can  also  be  used.  It  was,  however,  not  possible  to  wash  the  pre- 
cipitate free  of  electrolyte  with  water  or  even  ice  cold  water  without 
causing  it  to  pass  through  the  filter.  The  portion  which  ran  through 
was  not  white  but  yellow.  Ice  cold  water  is  more  satisfactory  than 
water  at  room  temperature.  When  it  is  desirous  to  wash  the  pre- 
cipitate free  of  acid  as  in  the  acidimetric  method  dilute  potassium 
nitrate  or  potassium  chloride  solutions  proved  satisfactory. 

The  following  method  is  proposed  for-  the  precipitaiton  of 
phosphorus  as  ammonium  phosphomolybdate,  and  for  the  deter- 
mination of  phosphorus : 

To  a  pure  phosphate  solution  containing  20-35  mg.  phosphorus 
in  a  volume  of  120  cc.,  5  g.  of  ammonium  nitrate  are  added.  To 


—22— 

the  cold  solution  are  added  rapidly  45  cc.  of  molybdate  solution 
(15  cc.  of  solution  I  poured  into  30  cc.  of  solution  II).  After  stir- 
ring the  solution  for  a  few  minutes  the  precipitate  forms  and  settles 
rapidly.  This  is  allowed  to  stand  from  4  hours  to  24  hours.  It  is 
often  convenient  to  filter  the  day  after  precipitating.  For  less  phos- 
phorus less  molyddate  solution  may  be  used.  The  precipitate  is 
dissolved  in  10  cc.  of  ammonium  hydroxide  and  the  phosphorus 
precipitated  with  magnesia  mixture  under  the  usual  conditions  and 
weighed  as  magnesium  pyrophosphate. 

The  completeness  of  precipitation  of  the  phosphorus  as  ammo- 
nium phosphomolybdate  was  tested  by  dissolving  the  precipitate  in 
ammonium  hydroxide  and  precipitating  the  phosphorus  with  mag- 
nesium acetate  solution  as  described  above. 

P  calculated  from  P  calculated  from  Difference 

KH2P04  taken  Mg.P.,0,  found 

.  0251  g.  "  .  0248  g.  — .  0003  g. 

.0232  .0229  —.0003 

.0281  .0281                                 .0000 

.0241  .024CT  —.0001 

.0490  .0489  —.0001 

.0457  .0457                                 .0000 

Average  deviation 0001 

To  test  the  effect  of  chloride  and  sulphate  in  solution  on  the 
precipitation  of  phosphorus  the  following  experiments  were  per- 
formed : 

1.  To  a  pure  phosphate  solution  as  above  5  grams  of  ammonium 
chloride  were  added  and  45  cc.  of  molybdate  solution  (15  cc.  of  the 
ammonium  molybdate  solution  I  poured  into  30  cc.  of  dilute  hydro- 
chloric acid  4:6).       After  filtering  and  washing  the  precipitate  it 
was  dissolved  and  the  phosphorus  precipitated  with  magnesia  mix- 
ture. 

2.  Same  as  1  except  that  nitric  acid  was  used  in  the  molybdate 
precipitating  reagent. 

3.  In  this  case  the  phosphate  solution  contained  5  grams  of 
ammonium  sulphate  and  the  precipitating  reagent  was  the  one  de- 
scribed in  this  paper  and  the  same  as  in  2. 

The  following  results  were  obtained: 

Method         P  calculated  from  P  calculated  from  Difference 

KH,P04  Mg2P,07  obtained 

1  .0240g.         '  .0239g.  —.0001 

2  .0244            .0243  —.0001 

3  .0259            .0258  —.0001 
3          .0240            .0239  —.0001 


-23-  , 

In  view  of  the  great  variations  in  the  results  of  precipitates  that 
were  dried  it  is  useless  to  weigh  the  ammonium  phosphomolybdate 
precipitate.  It  is  therefore  necessary  to  determine  phosphorus  in 
another'  way.  Hence  analyses  were  made  on  precipitates  without 
drying  them.  The  precipitates  were  obtained  from  known  weights 
of  phosphorus  as  follows: 

1.  To  the  pure  phosphate  solution  5  grams  of  ammonium  ni- 
trate were  added  in  a  volume  of  120  cc.    To  this  cold  solution  45  cc. 
of  molybdate  reagent  (15  cc.  of  solution  I  poured  into  30  cc.  of  solu- 
tion II)   were  added  rapidly.       After  the  precipitate  stood  it  was 
filtered,   washed  with  the  ammonium  nitrate,  nitric  acid  solution, 
dissolved  in  ammonium   hydroxide   and   reprecipitated  with   nitric 
acid  after  adding  2  cc.  of  ammonium  molybdate  solution  in  the  same 
volume  as  in  the  first  precipitation.     After  standing  again  it  was 
filtered  and  washed  as  before,  then  dissolved  in  ammonium  hydrox- 
ide and  analysed  as  described  previously  in  this  paper. 

2.  Same  as  1  except  that  5  grams  of  ammonium  chloride  were 
added  in  place  of  ammonium  nitrate. 

3.  Same  as  1  except  that  5  grams  of  ammonium  sulphate  were 
added  in  place  of  ammonium  nitrate. 

4.  Same  as  1  except  that  5  grams  of  ammonium  cholride  were 
added  in  place  of  ammonium  nitrate  and  hydrochloric  acid  was  used 
in  the  molybdate  reagent  in  place  of  nitric  acid. 

5.  Same  as  1  except  that  sulphuric  acid  was  used  in  the  molyb- 
date reagent  in  place  of  nitric  acid. 

The  following  results  were  obtained : 

P  calculated  P  calculated 

Exp.             Method             from  KH.,PO4  from  Mg2P,,O7  Molecular 

obtained  Ratio 

1  1          .0280g.  .0277g.  1:24.61 

2  1          .0233  .0230  1:24.63 

3  2          .0239  .0237  1:24.43 

4  2          .0241  .0238  1:24.64 

5  3         .0354  .0351  1:24.35 

6  4          .0229  .0228  1:24.41 

7  4         .0239  .0237  1:24.54 

8  5          .0234  .0232  1:24.33 

9  5         .0243  .0240  1:24.54 

Mean  molecular  ratio  1:24.50 


—24— 

These  experiments  show  that  the  presence  of  chloride  or  sul- 
phate in  solution  has  no  effect  on  the  completeness  of  the  precipita- 
tion of  phosphorus  and  also  that  the  yellow  precipitate  obtained 
under  these  conditions  is  one  in  which  the  ratio  of  phosphorus 
pentoxide  to  molybdic  oxide  is  constant.  The  average  deviation  of 
the  above  ratios  is  5  parts  per  1000.  The  results,  however,  do  not 
agree  with  the  generally  accepted  formula  where  the  ratio  of  phos- 
phorus pentoxide  to  molybdic  oxide  is  1 :  24. 

THE  VOLUMETRIC  METHOD 

By  referring  to  the  introduction  it  will  be  seen  that  the  acidi- 
metric  titration  method  for  the  determination  of  phosphorus  has 
always  been  surrounded  by  considerable  uncertainty.  These  uncer- 
tainties involve  the  choice  of  factor  which  of  course  depends  upon 
the  composition  of  the  ammonium  phosphomolybdate  precipitate, 
whether  or  not  the  ammonia  is  to  be  removed  before  making  the 
titration  and  the  choice  of  the  indicator  for  the  determination  of 
the  end-point.  Furthermore,  when  phenolphthalein,  which  is  the 
indicator  most  generally  proposed,  is  used  it  is  always  a  difficult 
matter  to  decide  when  the  end-point  is  reached  as  the  change  in 
the  indicator  is  very  gradual. 

In  order  to  proceed  intelligently  in  establishing  the  conditions 
for  the  acidimetric  titration,  electrometric  titrations  were  made  on 
solutions  containing  5  mg.  of  phosphorus.  The  precipitate  was  dis- 
solved in  a  known  volume  of  standard  sodium  hydroxide,  free  of 
carbonate,  placed  in  a  cell  and  the  hydrogen  ion  concentration 
measured  at  25 °C.  by  the  Saturated  Potassium  Chloride  Calomel 
Cell  Method  as  described  by  Fales  and  Mudge  (J.A.C.S.  42,  2434 
(1920). 

After  equilibrium  was  established,  0.25M  sulphuric  acid  was 
added  in  successive  portions  and  the  potentiometer  read  after  stir- 
ring the  solution.  About  five  minutes  elapsed  between  readings.  It 
was  not  possible  to  wait  for  the  solution  to  come  to  equilibrium  after 
each  addition  of  acid,  for  the  voltage  changed  continuously  for  sev- 
eral hours  and  the  solution  finally  turned  blue.  The  curves  given 
below  were  obtained  from  the  following  data  by  plotting  cubic 
centimeters  of  acid  added  as  abscissa  and  voltages  as  ordinates. 

These  titrations  were  repeated  on  similar  solutions  from  which 
the  ammonia  had  been  removed,  before  titration,  by  boiling  in  a 
current  of  hydrogen.  (See  curve  II). 


—25— 
Data  for  Curve  I 

(Solution  contained  5  mg.  of  Phosphorus,  titration  made  in  presence  of 

the  ammonia.) 

cc.  acid  added               voltage            cc.  acid  added  voltage 

0.0                         .9605                         4.0  .8269 

0.5                         .9540                         4.2  .7979 

1.0                         .9490                         4.4  .7628 

1.5                         .9436                         4.6  .7019 

2.0                         .9374                         4.8  .6630 

2.5  .9290                         5.0  .6395 
3.0                         .9160                         5.2  .6275 
3.2                         .9088                         5.4  .6196 
3.4                         .8986                         5.6  .6110 

3.6  .8832                         6.0  .5919 
3.8                         .8574 

Data  for  Curve  II 

(Solution  contained  5  mg.  of  Phosphorus,  titration  made  after  removing 

the  ammonia.) 


cc.  acid  added 

voltage 

cc.  acid  added 

voltage 

0.0 

.9440 

3.0 

.7932 

0.4 

.9372 

3.2 

.7530 

1.0 

.9253 

3.4 

.6871 

1.5 

.9102 

3.6 

.6607 

2.0 

.8823 

3.8 

.6458 

2.2 

.8654 

4.0 

.6341 

2.4 

.8488 

4.2 

.6285 

2.6 

.8322 

4.4 

.6203 

2.8 

.8150 

4.8 

.6020 

Data  for 

Curve  III 

(Solution 

contained  very  little  phosphorus.) 

cc.  acid  added 

voltage 

cc.  acid  added 

voltage 

0.0 

.9080 

1.6 

.6713 

0.2 

.8995 

1.8 

.6548 

0.4 

.8872 

2.0 

.6367 

0.6 

.8710 

2.2 

.6229 

0.8 

.8480 

2.4 

.6120 

1.0 

.8225 

2.6 

.6040 

1.2 

.7857 

2.8 

.5944 

1.4 

.7027 

3.0 

.5356 

None  of  the  curves  shows  a  sufficiently  pronounced  point  of 
inflection  to  yield  a  satisfactory  color  change  in  the  indicator  except 
in  the  case  of  Curve  III.  The  rather  indefinite  point  of  inflection 
does  occur  in  the  phenolphthalein  range  and  therefore  shows  that 
this  is  the  best  indicator  for  this  titration.  By  comparing  the  curves 
made  in  the  presence  (Curve  I)  and  absence  of  ammonia  (Curve  II), 


—26— 

it  is  seen  that  there  is  no  advantage  in  its  removal.  The  unsatisfac- 
tory form  of  the  titration  curve  is  certainly  due  to  the  presence  of 
phosphoric  acid.  In  the  case  of  Curve  III  where  the  solution  con- 


V0 


5"  6 

JL'TO  A 

tained  very  little  phosphorus  a  more  definite  point  of  inflection  was 
obtained  showing  that  the  method  is  more  satisfactory  for  very  small 
amounts  of  phosphorus. 

That  the  difficulties  encountered  in  titration  were  really  due  to 
the  presence  of  phosphoric  acid  rather  than  ammonia,  as  is  generally 


—27— 

assumed,  was  suggested  by  Fairchild  (J.  Ind.  Chem.  Eng.  4,  520 
(1912),  who  proposed  its  removal  by  precipitation  with  barium.  It 
should  also  be  noted  that  Hibbard  (J.  Ind.  Eng.  Chem.  5,  998 
(1913)  attributed  difficulties  to  the  presence  of  both  phosphoric 
acid  and  ammonia. 

As  a  result  of  this  work  it  has  been  shown  that  the  determina- 
tion of  phosphorus  in  quantities  of  10  mg.  or  over  is  best  accom- 
plished by  precipitation  with  the  ammonium  molybdate  solution 
which  has  been  described  and  under  the  conditions  which  have  been 
given.  The  precipitate  obtained  is  dissolved  and  the  phosphorus 
precipitated  by  magnesia  mixture  and  weighed  as  Mg2P2O7.  For 
quantities  of  phosphorus  less  than  10  mg.  the  weighing  of  such  small 
quantities  of  Mg2P2O7  becomes  inaccurate  and  the  use  of  the  acidi- 
metric  method  is  therefore  advocated. 

SUMMARY 

1.  A  new  determination  of  the  ratio  of  phosphorus  to  molyb- 
denum in  the  yellow  phosphomolybdate  precipitate  has  been  made  by 
a  new  method  of  analysis. 

2.  It  has  been  shown  that  the  composition  of  the  ammonium 
phosphomolybdate  precipitate  after  drying  is  so  variable  as  to  render 
the  gravimetric  determination  of  phosphorus  by  this  method  most 
unsatisfactory. 

3.  A  new  method  of  the  precipitation  of  phosphorus  as  ammo- 
nium phosphomolybdate  has  been  devised.  When  precipitated  by 
this  method  the  yellow  phosphomolybdate  precipitate  as  formed  in 
solution  shows  a  constant  ratio  of  phosphorus  pentoxide  to  molybdic 
oxide  which  is  1 : 24.50  with  a  mean  deviation  of  5  parts  per  1000. 

4.  It  has  been  shown  that  this  ratio  remains  constant  even  when 
large  concentrations  of  chloride  or  sulphate  are  present  in  the  solu- 
tion from  which  the  phosphomolybdate  forms. 

5.  It  has  been  shown  that  under  the  conditions  given  for  the 
formation  of  ammonium  phosphomolybdate  no  complexes  with  sul- 
phates or  chlorides  are  produced. 

6.  Electrometric  titrations  of  yellow  phosphomolybdate  precipi- 
tates have  been  made.    The  curves  plotted  from  these  results  have 
not  thus  far  appeared  in  the  literature  and  have  furnished  a  rational 
method  for  the  acidimetric  estimation  of  phosphorus  with  a  deter- 
mination of  its  limitations. 

7.  Accurate  methods  for  the  determination  of  phosphorus  have 
been  described  with  the  limitations  under  which  they  can  be  used. 


FIT  A. 

Norma  E.  Johann  was  born  in  New  York  City,  January  9,  1893. 
In  1914  she  received  the  degree  of  A.B.  from  Hunter  College  where 
she  taught  in  the  Department  of  Chemistry  two  years  following 
graduation.  She  has  held  the  position  of  Assistant  in  Chemistry  at 
Columbia  University  since  1917.  She  was  a  graduate  student  in  the 
Department  of  Chemistry,  Columbia  University,  during  the  sum- 
mers of  1915  and  1918  and  during  the  academic  years  1914-15, 
1915-16,  1916-17,  1917-18,  1918-19,  1919-20,  and  1920-21.  In  1917 
she  received  the  degree  of  A.M. 


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